This invention relates to a novel unsaturated imide compound which is well soluble in an organic solvent and gives a cured product excellent in heat resistance, low water absorbability and flexibility; a process for producing the unsaturated imide compound; and an intermediate therefor.
A thermosetting resin composition comprising the above unsaturated imide compound as a main component can be used as a laminate, sealing material, insulating material, sliding material and other molding materials in the electric and electronic fields.
This invention is also concerned with a dinitro compound and a diamino compound which are intermediates for producing the above unsaturated imide compound.
Heretofore, electric and electronic parts such as semiconductor and the like have been sealed with an epoxy resin. This is because the sealing with an epoxy resin is more economically advantageous than hermetic seal system using glass, metal and ceramic. However, the recent trend is that the conditions for use of electronic parts become severe. For example, the fabrication method is now switching from insert fabrication to surface fabrication, and this is accompanied by a result that sealing materials per se are exposed to solder bath temperatures. Consequently, the sealing material is required to have excellent heat resistance; however, epoxy resins do not sufficiently satisfy the requirement for heat resistance.
Thermosetting polyimide resin-sealing has been proposed for the purpose of obtaining high heat resistance. For example, 4,4'-diphenylmethane bismaleimide has been known as a bismaleimide type thermosetting resin. The cured product of this compound is excellent in heat resistance, but is brittle and high in hygroscopicity. Also, this compound has a low solubility in general purpose organic solvents and it is difficult to prepare a varnish therefrom in the formation of a laminate or the like.
The known general method for preparing unsaturated imide compounds is a chemical ring-closure method which comprises reacting an aromatic amine solution with a solution of an acid anhydride such as maleic anhydride or the like, and then allowing a dehydrating agent to act thereon [U.S. Pat. No. 2,444,536; Org. Synth., 41, 93 (1961) and the like]. However, this method has a tendency that acetic acid, though in a slight amount, remains in the product and hence acetic acid odor becomes a problem when the product is cured at a high temperature. Impurities due to acetic acid tends to be produced under some conditions, whereby the purity of product is lowered. Many proposals have been made for solving this problem. A typical example thereof is a method comprising reacting an aromatic amine solution with a solution of an acid anhydride such as maleic anhydride or the like, and then heat-dehydrating the resulting amic acid solution to cause ring-closure (for example, Japanese Patent Kokoku No. 55-46,394, Japanese Patent Application Kokai No. 60-11,465 and the like). According to this method, no acetic acid is produced, and hence, there is no problem due to acetic acid. However, since unsaturated imide compounds which are thermosetting resins are exposed to high temperature during curing, there are such problems that a high molecular weight product and gel are produced depending upon the reaction conditions and the structure and reactivity of the imide, whereby the purity of product is lowered and the still is contaminated. When the reaction conditions are made mild for solving the above problems, the reaction time must be greatly prolonged.